Hello,
Eventually this solution solved my problem. There is only one thing you should consider. In the example, the page id number is mentioned. At first I changed this id number to the page title:
if($sidebar_r == ‘off’ || is_page(shop))
This doesn’t solve the problem, you MUST use the page id number in the functions.php and MUST NOT use the page name.
With the assistance of the theme developer we found that out.
Now my page looks like this and I am satisfied:
https://www.doordebenen.nl/shop-2/